This application incorporates by reference of Taiwan application Serial No. 090115493, filed Jun. 26, 2001.
1. Field of the Invention
The invention relates in general to a motor driving apparatus, and more particularly to a stepping motor driving apparatus.
2. Description of the Related Art
The motor has been the core of almost every automation apparatus. In order to correspond with different requirements for using in different environments, several kinds of motors having different properties have been developed. Some of them possess the advantage of high-efficiency while some of them fulfill the requirement of speed and positioning. Among several types of motors, the stepping motor plays an important role in the controlling system due to its steady speed and precise positioning. Therefore, the way to accurately control the dynamic property has become a very important issue.
There are two types of commonly used stepping motor: PM (Permanent Magnet) motors and Hybrid motors. Besides, the constant voltage driver and the constant current driver for the stepping motor are in common use. Since the constant current driver uses an extra set of switching transistors to eliminate the need for two power sources and offers high performance and high efficiency in operation, it therefore becomes by far the most widely used driver for industrial applications. Hence, the constant current driving of the stepping motor is taken as an example as the following. Referring to FIG. 1, the block diagram of a conventional stepping motor driving apparatus shows the coupling relation among components. Conventionally, the motor controller 120 is used for controlling the operation of the stepping motor 150. In practice, the control signal CT is first sent to the motor controller 120. The clock signal CK for operating the stepping motor 150 is generated by the motor controller 120 according to the content of the control signal CT, and then sent to the motor driver 140. After receiving the clock signal CK and reference voltage Vr, the motor driver 140 generates the corresponding driving signal 145 according to the two signals CK and Vr. The driving signal 145 is used for controlling the operation of the stepping motor 150. Since the motor driver 140 is a constant current driver, the reference voltage Vr is received and converted into the driving current by the motor driver 140 for driving the current accordingly. The operation property of the stepping motor will be illustrated as follows with reference to the accompanying drawings.
Referring to FIG. 2, the operation property of a stepping motor driven by a rated current is shown. The x-coordinate represents the clock frequency, which is the frequency of clock signal CK, while the y-coordinate represents the torque value of the stepping motor. The curve on the graph indicates the variation of the torque of the stepping motor corresponding to the change of the clock frequency when the stepping motor 150 is driven by the constant current I. The torque of the stepping motor is T1 while the clock frequency is f1 and the torque of the stepping motor is T2 while the clock frequency is f2. As shown in FIG. 2, the clock frequency increases as the torque of the stepping motor decreases. The higher clock frequency means the higher motor speed. Therefore, in the condition of constant driving current I, the motor speed increases as the torque of the stepping motor decreases so that the load capacity of the motor reduces.
Conventionally, the clock signal CK of the motor controller 120 is the signal for controlling the stepping motor 150. As shown in FIG. 1, it might cause the damage of the stepping motor when the motor controller is abnormal. For example, the stepping motor operates at a high speed and the system fails due to the bug or unusual operating procedures. The stepping motor might probably run stiff and then too much current will cause excessive heating and damage to the motor windings and even destroy the stepping motor. By design, reducing the current flow to the motor by a small percentage will smooth the rotation. However, the maximum of the driving current has to be reduced accordingly. It decreases the maximum speed of the system and the efficiency of the stepping motor, which might be quite uneconomical.
It is therefore an object of the invention to provide a stepping motor driving apparatus with dynamic torque control, improving the vibration on the motor by the adjustment of the driving current and raising the rate of power usage.
It is another object of the invention to provide a stepping motor driving apparatus with dynamic torque control, avoiding destroying the stepping motor by the protection of over-current flow while the system fails.
The invention achieves the above-identified objects by providing a stepping motor driving apparatus with dynamic torque control, capable of driving a stepping motor. The stepping motor driving apparatus includes a motor controller, a motor driver, and a frequency-to-voltage converter. After receiving a control signal, the motor controller generates a corresponding clock signal according to the type of the control signal and outputs a clock signal to the motor driver and the frequency-to-voltage converter. The frequency-to-voltage converter receives the clock signal, generates a reference voltage corresponding to the frequency of the clock signal, and outputs the reference voltage to the motor driver. After the motor driver receives the clock signal from the motor controller and the reference voltage from the frequency-to-voltage converter, the motor driver generates a corresponding driving current accordingly and uses the clock signal and driving current to control the operation of the stepping motor.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.